Thermal Tolerance of American Lobster (Homarus americanus) Larvae and Post-Larvae: Understanding the Physiology of Vulnerable Life Stages in a Changing Climate.

Jane, Aubrey¹*, Jesica D. Waller², Douglas B. Rasher³, Eric Annis⁴, Markus Frederich¹, ¹University of New England, Biddeford, ME, ²Maine DMR, East Boothbay, ME, ³Bigelow Laboratory for Ocean Sciences, East Boothbay, ME, ⁴Hood College, Frederick, MD

The American lobster is an ecologically and economically important species in the Gulf of Maine. Climate change is reshaping its biogeography; therefore, understanding the physiology of this species is required to predict future range shifts. While the thermal tolerance of adult lobsters is well studied, thermal tolerances of the earliest developmental stages, which ultimately dictate settlements and recruitment for the fishery, remain understudied. Previous research has used only lab-reared larvae. We reared lobsters up to stage IV and exposed them to acute (4°C-32°C) or chronic (8°C-26°C) temperature treatments in each stage. Post-larvae were also caught in the wild to allow for comparisons between lab-reared larvae and natural populations. Critical temperatures, defined by a complete lack of scope for activity after acute (20-minute) exposure, were reached at 4 and 32°C in stages I and II; 8 and 32°C in stage III, and 8 and 26°C in stage IV. Wild stage IV lobsters reached critical temperatures at 4°C and 32°C. These ontogenetic shifts in thermal tolerance, as well as the discrepancy between lab and wild lobsters, were corroborated by chronic exposure assays and molecular data. The reduced thermal tolerance of lab-reared larvae suggests an important limitation in our current knowledge of the thermal tolerance of larval stages. Such results have important implications for understanding the drivers of settlement patterns, and therefore species distribution in a changing climate.